NITROGEN #1 NITROGEN #1
•• NOxNOx and NHand NH33 emissions, NOxemissions, NOx depositiondeposition
•• Nitrogen in fuelsNitrogen in fuels
•• Formation and reduction of Formation and reduction of NOxNOx during burner combustionduring burner combustion
•• Low Low NOxNOx technology : low NOxtechnology : low NOx burners, fuel/air staging, ...burners, fuel/air staging, ...
•• Flue gas treatment for NOxFlue gas treatment for NOx reduction: SCR, SNCR, otherreduction: SCR, SNCR, other
NOTE :
NOTE : NOxNOx = NO + NO= NO + NO22
see:
see: www.hut.fi/~rzevenho/gasbookwww.hut.fi/~rzevenho/gasbook
Nitrogen emissions and deposition in Europe Nitrogen emissions and deposition in Europe
NOxNOx emissions 1994emissions 1994 (tonnes N)
(tonnes N) NHNH33 emissions 1994emissions 1994 (tonnes N)
(tonnes N) NHNH33 + NOdepositions+ NOdepositions 1994 (mg N/m²) 1994 (mg N/m²)
NN22O as greenhouse gasO as greenhouse gas
and in ozone layer depletion and in ozone layer depletion
Global sources of N
Global sources of N22OO
Emissions of nitrogen compounds Emissions of nitrogen compounds
and human activities and human activities
Sources for NOx Traffic ~60 %
Fossil fuel-fired heat and power ~30 %
Industry ~10 %
Sources for NH3 Agriculture ~80 %
Sources for N2O Fossil fuel-fired heat and power ~30 % Forest fires, landgain, ….. ~60 % Industry (e.g. adipic acid production) ~10 %
Nitrogen
Nitrogen--containing containing structures in solid fossil structures in solid fossil
fuels and biomass fuels and biomass
Nitrogen in of fuels (dry %
Nitrogen in of fuels (dry %--wt)wt)
Fossil fuels Biomasses & waste - derived fuels
Coal 0.5 – 3 Wood 0.1 – 0.5
Bark ~ 0.5
Oil < 1 Straw 0.5 – 1
Natural gas 0.5 – 20
Light fuel oil ~ 0.2 Sewage sludge ~ 1
Heavy fuel oil ~ 0.5 Car tyre scrap ~ 0.3
Municipal solid waste (MSW) 1 – 5
Peat 1 – 2 Refuse derived fuel
(RDF) ~ 1
Packaging derived fuel (PDF) ~ 1
Petroleum coke ~ 3 Auto shredder residue (ASR) ~ 0.5
Leather waste ~ 12
Orimulsion™ ~ 4 Black liquor solids 0.1 - 0.2
NOxNOx (NO(NO22))
emission emission standards standards
for EU for EU
Solid Fuels Solid Fuels
(directive (directive 2001/80/EC) 2001/80/EC)
Fuel New /
Existing* Plant size
(MWth) Emission standard
(mg/m3STP dry) Comments Solid** Existing 50 - 500 600 @ 6% O2
“ “ > 500 500 @ 6% O2 Until 1.1.2016; if after 1.1.2008 < 2000 h/y
then 600 @ 6% O2
“ “ > 500 200 @ 6% O2 After 1.1.2016; if < 1500 h/y then 450 @ 6% O2
Solid, general New 50 - 100 400 @ 6% O2
“ “ 100 – 300 200@ 6% O2 “Outermost regions”
300 @ 6% O2
“ “ > 300 200 @ 6% O2
Solid, biomass New 50 - 100 400 @ 6% O2
“ “ 100 – 300 200@ 6% O2
“ “ > 300 200 @ 6% O2
* Existing = plant existing on Nov. 27, 2002 ; or license for new plant requested before that date and plant entering operation before Nov. 27, 2003
** Plants that operated during year 2000 on solid fuels with a volatile content less than 10 %-wt follow a limit of 1200 mg/m3STP dry @ 6% O2 until 1.1.2018
*** Applies only to > 70 % load and > 500 h/y operation. Limit is 75 mg/m3STP dry @ 15 % O2 for CHP plants > 75 % overall efficiency; combined cycle plants > 55 %
electrical efficiency, or mechanical drives. Other, single cycle gas turbines, with efficiency η > 35 % follow the limit value 50× η/35 mg/m3STP dry @ 15 % O2
NOxNOx (NO(NO22))
emission emission standards standards
for EU for EU
Liquid and Liquid and
Gaseous Gaseous
Fuels Fuels
(directive (directive 2001/80/EC) 2001/80/EC)
Fuel New /
Existing*
Plant size (MWth)
Emission standard (mg/m3STP dry)
Comments
Liquid Existing 50 - 500 450 @ 3% O2
“ “ > 500 400 @ 3% O2
Liquid New 50 – 100 400 @ 3% O2
“ “ 100 – 300 200 @ 3% O2 “Outermost regions”
300 @ 6% O2
“ “ > 300 200 @ 3% O2
Liquid New > 50 120 @ 15 % O2 Gas turbines ***
Gas Existing 50 - 500 300 @ 3% O2
“ “ > 500 200 @ 3% O2
Gas, natural New 50 – 300 150 @ 3% O2
“ “ > 300 100 @ 3% O2
Gas, other New 50 – 300 200 @ 3% O2
“ “ > 300 200 @ 3% O2
Natural gas New > 50 50 @ 15 % O2 Gas turbines ***
Other gas New > 50 120 @ 15 % O2 Gas turbines ***
* Existing = plant existing on Nov. 27, 2002 ; or license for new plant requested before that date and plant entering operation before Nov. 27, 2003
** Plants that operated during year 2000 on solid fuels with a volatile content less than 10 %-wt follow a limit of 1200 mg/m3STP dry @ 6% O2 until 1.1.2018
*** Applies only to > 70 % load and > 500 h/y operation. Limit is 75 mg/m3STP dry @ 15 % O2 for CHP plants > 75 % overall efficiency; combined cycle plants > 55 % electrical efficiency, or mechanical drives. Other, single cycle gas turbines, with efficiency η > 35 % follow the limit value 50× η/35 mg/m3STP dry @ 15 % O2
NOxNOx (NO(NO22))
emission emission standards for standards for
waste (co
waste (co--) ) firing and firing and
cement cement
plants for EU plants for EU
(directive (directive 2000/76/EC) 2000/76/EC)
CCcoco--firingfiring = (= (VVwastewaste . C. Cwastewaste + + VVprocessprocess.C.Cprocessprocess)/( )/( VVwastewaste + V+ Vprocessprocess), V = exhaust volume ), V = exhaust volume
Type of plant Plant Emission standard
(mg/m3STP dry) Comments Waste incineration < 6 t /h 200 @ 10 % O2 * Daily average
“ > 6 t /h 400 @ 10 % O2* Daily average Cement, incl. co-firing All 800 / 500 @ 10 % O2 Existing / new **
Waste co-firing *** 50 – 100 MWth Cprocess 400 @ 6 % O2 Solid fuel
“ “ Cprocess 350 @ 6 % O2 Biomass
“ “ Cprocess 400 @ 3 % O2 Liquid fuel
“ 100 – 300 MWth Cprocess 300 @ 6 % O2 Solid fuel
“ “ Cprocess 300 @ 6 % O2 Biomass
“ “ Cprocess 400 @ 3 % O2 Liquid fuel
“ > 300 MWth Cprocess 200 @ 6 % O2 Solid fuel
“ “ Cprocess 300 @ 6 % O2 Biomass
“ “ Cprocess 400 @ 3 % O2 Liquid fuel
* Various exceptions until 1.1.2008 or 1.1.2010, and until 1.1.2007 these regulations do not apply to hazardous waste incineration
** Existing = plant existing on Dec. 28, 2002; or license for new plant requested before that date and plant entering operation on Dec. 28, 2003 or Dec. 28, 2004.
Until 1.1.2008 special regulation 1200 mg/m3STP dry @ 10 % O2 for existing wet kilns and small kilns co-firing less than 3 t waste /h.
*** Various exceptions until 1.1.2008 for existing fluidised beds 100 – 300 MWth that burn solid fuels or biomass provided that Cprocess < 350 mg/m3STP dry @ 6 % O2. Until 1.1.2007 these regulations do not apply to hazardous waste incineration
NO formation in pulverised coal, oil and NO formation in pulverised coal, oil and
natural gas firing natural gas firing
Thermodynamics Thermodynamics
versus versus
measurements measurements
Time (s)
Concentration (ppmv)
Kinetic modelling of coal
Kinetic modelling of coal pyrolysispyrolysis gas gas combustion
combustion
Combustion in Combustion in
plug flow reactor (PFR).
plug flow reactor (PFR).
850°C, 1 bar.
850°C, 1 bar.
Initial gas (%
Initial gas (%--volvol):):
8% CO, 3% H
8% CO, 3% H22, 2% H, 2% H22OO 0.05% HCN, 8% O
0.05% HCN, 8% O22, 73%N, 73%N22
NO Formation from N
NO Formation from N22 Fixation: NFixation: N22 →→ NONO
n:o Reaction
1 Thermal NO N2 + O → NO + N N + O2 → NO + O N + OH → NO + H
2 Prompt NO
N2 + CH → HCN + N
+O +H +H +O2,+OH
HCN ⎯→ NCO ⎯→ NH ⎯→ N ⎯⎯⎯⎯→ NO
3 Formation via N2O intermediate O + N2 + M → N2O + M
N2O + O → 2NO
Kinetic modelling of NO formation:
Kinetic modelling of NO formation:
thermal
thermal NOxNOx, prompt , prompt NOxNOx, N, N22OO--NONO
Methane combustion with air in a stirred reactor (CSTR), at 1 ba
Methane combustion with air in a stirred reactor (CSTR), at 1 bar, air factor r, air factor λλ = 1.15= 1.15
NO formation mechanisms:
NO formation mechanisms:
effect of air factor, effect of air factor, λλ
Methane combustion Methane combustion
with air with air
in a stirred reactor in a stirred reactor
(CSTR), (CSTR), at 1 bar, at 1 bar,
residence time 4 ms.
residence time 4 ms.
Release of Fuel
Release of Fuel--N during N during pyrolysispyrolysis of Australian coal
of Australian coal
TAR HCN
NH3
Bayswater coal
Yallourn coal Millmerran
coal Blair Athol
coal
HCN
Oxidation of volatile fuel
Oxidation of volatile fuel--N compoundsN compounds during burner combustion
during burner combustion (simplified)(simplified)
fuel
fuel -- NN volatilesvolatiles--NN
NHNH33
HCNHCN HHiiNCONCO
NHNHii
NONO
NN22
+O, +OH +O, +OH
+H+H
+O+O22, +OH,+O, +OH,+O oxidising oxidising
+NO, +
+NO, +NHNHii reducing reducing +O+O22, +OH, +O, +OH, +O
char char -- NN
Principle of air staging.
Principle of air staging.
Assumed: char
Assumed: char-N gives NO (40%) and N-N gives NO (40%) and N22 (60%),(60%), NNfixfix = all nitrogen compound except N= all nitrogen compound except N22
primary zone (SR < 1)
secondary air
fuel + primary
air
secondary zone (SR >1)
primary zone (SR < 1) secondary zone
(SR > 1) primary zone
(SR < 1) fuel
char fuel +
transport air
primary air secondary air
secondary zone (SR > 1) primary zone
(SR < 1)
Time
Concentration
Oxidation of fuel
Oxidation of fuel--N to NO and NN to NO and N22 during during burner combustion with significant char
burner combustion with significant char--N N
(simplified) (simplified)
fuel
fuel -- NN
volatile
volatile-- NN
char
char -- NN
HCN, NH HCN, NH33
NONO
NN22
oxidising oxidising
reducing reducing y = 20 ~ 80%
y = 20 ~ 80%
100 %
100 % -- yy NN22 NONO
Thermal
Thermal NOxNOx, prompt , prompt NOxNOx, fuel , fuel NOxNOx
Time
Concentration
primary zone (SR > 1)
fuel + primary
air
primary zone (SR > 1)
secondary stage (SR < 1)
secondary stage (SR < 1)
secondary fuel final
combustion air
final combustion zone (SR > 1)
final combustion
zone (SR > 1) primary zone
(SR > 1)
secondary stage (SR < 1) final combustion
zone (SR > 1)
fuel + transport
air primary air secondary
fuel
fuel
final combustion
air
Principle of fuel staging.
Principle of fuel staging.
Assumed: fuel NO and thermal NO formed during primary stage, Assumed: fuel NO and thermal NO formed during primary stage,
NNfixfix = all nitrogen compound except N= all nitrogen compound except N22
Reburning Reburning technology technology
Main
Main NOxNOx formation and decomposition formation and decomposition reactions during burner combustion
reactions during burner combustion
(summary) (summary)
Pulverised fuel combustion furnace types Pulverised fuel combustion furnace types
←← ←← Front wall Front wall
fired fired
←←
Opposed wall Opposed wall
fired fired
→→
Tangential / Tangential /
corner corner
fired fired
A typical A typical pulverised coal
pulverised coal--firingfiring flame
flame
Typical
Typical NOxNOx emissions for emissions for various types of various types of
coalcoal--fired fired furnaces as furnaces as
function of unit function of unit
sizesize
Note : 1 lb/MBTU ~ Note : 1 lb/MBTU ~
0.5 mg/GJ 0.5 mg/GJ
NSPS = New Source Performance Standard NSPS = New Source Performance Standard
WallWall--fired fired burner burner
combustion combustion
and and
tangential tangential combustion combustion
(T(T--firing)firing)
LowLow--NOxNOx burners for burners for pulverised coal firing pulverised coal firing
IFRF flame type IFRF flame type classification system classification system
Reverse flow leads to rapid ignition close Reverse flow leads to rapid ignition close to the burner, resulting in NO reduction.
to the burner, resulting in NO reduction.
Sufficient penetration and time in IRZ is Sufficient penetration and time in IRZ is
crucial !!!!!!
crucial !!!!!!
Stoichiometry
Stoichiometry in primary zone:in primary zone:
λλ ~0.6 .. 0.7 is optimal~0.6 .. 0.7 is optimal λλ > 0.7 gives more NO> 0.7 gives more NO
λλ < 0.6 gives more NH< 0.6 gives more NH33, HCN,... giving , HCN,... giving more post
more post--flame NOflame NO Stoichiometry
Stoichiometry ↓↓ then NO ↓then NO ↓ ,, but carbon
but carbon--inin--ash ash ↑↑ and corrosion ↑and corrosion ↑
LowLow--NOxNOx concentric firing system (LCNFS™)concentric firing system (LCNFS™)
Overfire
Overfire air (OFA) and advanced OFAair (OFA) and advanced OFA
Air and fuel Air and fuel staging for
staging for NOxNOx control
control
Overview of Overview of
LowLow--NOxNOx technologies technologies
for burner for burner combustion combustion
Overview of Low
Overview of Low NOxNOx technologiestechnologies
Advantageous when Problems
Low excess air When excess air is used Fuel burnout decreases Air staging / over-fire air In principle always Limited effect,
increased risks for corrosion, fouling, slagging Low NOx burner
i.e. in-flame staging
In principle always Fuel burn-out decreases, not a big problem, however Fuel staging i.e.
reburning with coal, oil, natural gas
In principle always, especially when the reburn fuel is also the start-up fuel
Capital cost of system modifications Flue gas recirculation High temperature oil- or
gas-fired furnaces Low efficiency if not combined with other
method
Relative effects of Low
Relative effects of Low--NOxNOx technologiestechnologies
NOxNOx emissions model for emissions model for HemwegHemweg 8 plant8 plant
600 MWe600 MWe, tangential, 1993, 535°C/568°/230 bar (between Amsterdam and , tangential, 1993, 535°C/568°/230 bar (between Amsterdam and HaarlemHaarlem))
Selective catalytic Selective catalytic reduction (SCR) of
reduction (SCR) of NOxNOx /1/1
Selective catalytic Selective catalytic
reduction (SCR) reduction (SCR)
of of NOxNOx /2/2
Efficiency and ammonia slip ( Efficiency and ammonia slip (↑↑))
and catalyst activity ( and catalyst activity (→→))
A damaged SCR unit: damaged catalyst A damaged SCR unit: damaged catalyst
Selective Non
Selective Non--catalytic catalytic NOxNOx reduction (SNCR)reduction (SNCR)
Effect of temperature
Effect of temperature Effect of CEffect of C22HH66 additionaddition + + CC22HH66
NOxNOx removal from flue gases : other methodsremoval from flue gases : other methods
•• Copper oxide process for simultaneous Copper oxide process for simultaneous DeSOxDeSOx / DeNOx/ DeNOx
•• dry absorption on activated carbon at ~220ºC :dry absorption on activated carbon at ~220ºC :
NOxNOx + SO+ SO22 + carbon + H2O + O2+ carbon + H2O + O2→→ NN22 + H+ H22SOSO44
•• Wet scrubbing with water after oxidation of NOWet scrubbing with water after oxidation of NO Gas phase: NO + O
Gas phase: NO + O22 →→ NONO22, N, N22OO44, N, N22OO55, HNO, HNO22 Liquid phase: NO
Liquid phase: NO22, N, N22OO44, N, N22OO55, HNO, HNO22+ H2O + H2O →→ HNOHNO33
•• Wet scrubbing with “chemical enhancement” (Wet scrubbing with “chemical enhancement” (NaOHNaOH, KMnO4), KMnO4)
•• Electron beam irradiationElectron beam irradiation
•• Phosphorous : catalyses oxidation of NO to NOPhosphorous : catalyses oxidation of NO to NO22
